technical features
80 DECEMBER 2011 water
small wastewater systems
One of the most difficult requirements
of JS 895/2006 is the nitrate-nitrogen
requirement. An initial feasibility study
for the SCP identified that sand filters
(either intermittent or recirculating),
followed by reed beds, offered the most
favourable low-maintenance technology
capable of providing consistent oxidation
of the high-strength ammonia-nitrogen
concentrations present in the raw
septage.
However, in order for the sand filters
to operate properly, unit operations were
necessary upstream to reduce organic
and solids loading rates. Sizing and unit
process design of the treatment facilities
was based primarily on operational
data and operating experience obtained
from Drarga, Morocco, with adaptations
necessary to accommodate the more
concentrated nature of septage and
the differing environmental conditions.
The primary differences between the
two facilities are the capacity (Shobak
is designed to handle up to 450m3/d,
while North Shouneh is designed for
1,200m3/d), and the local climate
conditions (Shobak is designed for a
winter average temperature of 6.4°C,
while North Shouneh is designed for a
winter average temperature of 15.8°C).
Shobak WWTP
The Shobak WWTP is designed to receive
an annual average of 350m3/d. The facility
has been designed to accept an average
of 425m3/d over eight summer months and
200m3/d over four winter months, with the
ability to treat high flows of up to 450 m3/d
for at least one summer month. Because of
the cold winter temperatures encountered
in the Shobak region, complete nitrification
and denitrification using natural processes to
continuously meet JS 895/2006 was deemed
uneconomical under design conditions.
Therefore, the Shobak WWTP was designed
primarily for effluent evaporation.
The Shobak WWTP for the treatment
of septage uses natural, low-technology
treatment provided by the following key
process units: septage receiving and
screening station; two settling/digestion
reactors (each consisting of four 170m2
settling/digestion compartments); two
2,900m2 anaerobic settling lagoons; 10
300m2 intermittent sand filters; four 5,000m2
reed beds; and 30,000m2 of evaporation
ponds (see Figure 3). The settling/digestion
reactors and anaerobic lagoons were
designed for a 5.0 day and 20 day HRT
respectively. Five sand filters are dosed
once per day at an average rate of 350mm.
Although primarily designed for
evaporation of the effluent, current
treatment is capable of meeting reuse
standards during parts of the year,
particularly under lower loading rates
than design. The facility has also been
sited and designed to accommodate
upgrade and expansion in the future
should it be necessary.
The facility started receiving septage
in late January 2010 and one treatment
train became filled and began completely
processing wastewater at the beginning
of July 2010. During the first 12 months of
operation (February 2010 through January
2011) an average of 164 tankers delivered
septage each month for an average
influent quantity of 64m3/d. The highest
septage quantities were received in June
and July (maximum monthly average
of 85m3/d). Plant performance data is
presented in Table 5.
Comparing the effluent quality results
presented above against the Jordanian
Irrigation Reuse Standards (JS893/2006)
shown in Table 4, the average quality of
effluents produced by the WWTP is in
compliance with Class A. However, some
of the samples taken (i.e., maximum
values) exceeded Class A limits. All
Table 5. Shobak WWTP performance (November 2010 through January 2011).
Parameter
Influent
(mg/l)
Settling/
Digestion
(mg/l)
Anaerobic
Lagoon
(mg/l)
Sand Filters
(mg/l)
Reed Beds
(mg/l)
Removal
Efficiency
BOD
2,270.4
563.8
312.6
75.6
22.6
99.0%
COD
4,515.4
1,070.4
704.0
172.0
70.2
98.4%
TSS
2,048.0
492.4
354.0
129.0
20.0
99.0%
TN
292.0
207.5
170.7
37.9
8.2
97.2%
NO3-N
2.3
2.4
2.1
13.8
4.4
PO4
25.1
N/A
N/A
N/A
1.0
96.0%
TDS
2,003
2,160
2,191
2,107
2,489
Fecal Coliform
(MPN/100ml)
4.8 x108
N/A
N/A
N/A
25.6
Nematodes
(eggs/5l)
N/A
N/A
N/A
N/A
0
Septic hauler unloading at Shobak.